How It Works: Designing car interiors

Jennifer Fravica, Driving

Beyond merely looking nice, a car interior also must be functional and durable

by
Jil McIntosh | October 11, 2017

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Mention automobile design, and most people think of someone drawing a sketch of the exterior. But the interior must be styled and created as well, and it requires the same level of attention to detail, as well as practicality and comfort, as anything on the outside.

“We do a lot of technical research into innovations,” says Kerstin Schmeding, interior designer for BMW and Mini. “We look at the latest trends in materials, in colour and trim. The car has to be fun and nice, but it also has to be functional.”

As with exterior designs, the interior begins with sketches. These are first done on paper, and then with computer-aided design (CAD). The most promising proposals are then rendered in clay. Although clay models date back to the 1930s, they’re still considered essential, even in the age of computers. “We need clay because it’s a physical car,” Schmeding says. “Once you see it in reality, you see things in the proportion that you don’t recognize in a virtual model. Then you tweak it, and it’s like a dialogue between the digital and clay processes, going back and forth.”

2017 Mini John Cooper Works Convertible

Interior design is especially challenging because of everything that goes into it. The seats must fit a wide range of drivers and occupants. There must be enough switches to control the features, and they have to be easy enough to reach and use. The designers have to decide on colours and fabric for the seats, and the type of carpet to use.

They must also incorporate safety features such as airbags, including in the seat sides and above the side windows. The airbag for the front-seat passenger requires a specialized panel in the dash, fitted with thin material so the deploying airbag can push through it. Depending on the design, the panel may be on a seam line to help hide it, but on a plain dash, the cover must fit so that the small indentation behind it doesn’t show.

The interior design has to match the theme of the car, and a luxury sedan will have a different look from a sporty convertible or a family van. This will also affect the materials used: the pricier models will probably have soft leather upholstery, while a less-expensive family car will have child-friendly, easy-to-clean seats.

No matter what the fabric, the seat upholstery has to last through occupants getting in and out thousands of times. Most seats will usually have extra-durable material on the side of the cushions where people slide into the vehicle, as well as on the console and door panels where occupants rest their arms. All materials are tested extensively, including for abrasion, colour fading, and how they perform in extreme heat, cold, or humidity.

If there’s a pattern in the fabric, it must be chosen carefully. If it’s too big, it draws too much attention. “It’s a lot of gut feeling,” Schmeding says. “You see something and you know that it’s wrong. Colours have to work with the environment and with the texture of the material. If the colour is too intense or too moody, you don’t get the right expression, or it can look dirty or old.”

Even leather can differ, depending on the vehicle. Cowhide naturally has blemishes or scars. Some pricier cars have plain leather, which looks luxurious but creates expensive waste when panels are cut around the flaws. A more cost-effective approach is to emboss a pattern into the leather, hiding the marks so the whole hide can be used. It’s a lot of work to design a grain that looks good throughout, since the design can distort and look bad when it’s wrapped around curved panels. The designers work with the leather supplier throughout the process to see how the finished leather performs.

The latest Rolls-Royce Phantom VIII has a choice of custom interior designs.

Carpet is not just part of the design, but also performs the function of minimizing road noise inside the cabin. It must be capable of being pressed into extreme shapes that will lie flat across the floor and up the sides of the centre console. Interior designers have to consider the type of yarn and how tightly the carpet is woven, to avoid the weave opening up where it’s stretched over a contour. Non-woven material is usually used in the trunk, and these fabrics must be especially durable and easy to clean after coming in contact with shoes and cargo.

Interior materials must be functional, but designers also have to consider their weight in light of fuel economy standards. “Each piece doesn’t seem so important, but everything together adds up, so we look into different materials,” Schmeding says. “Leather is heavy, so we can make a seat that’s leather in combination with fabric, and it’s a nice design but also contributes to the weight of the car.”

Designers always look beyond automotive for inspiration, but Schmeding says that while her team considers fashion styles, furniture trends are more useful because they don’t change as quickly. “It’s a long process, and we can’t develop within months like fashion does,” she says. “It’s always a balance between the technical and the design aspects.”